It’s no secret. The future of digital music is downloadable files stored on some sort of magnetic memory. For now it’s the ubiquitous hard drive or SSD memory. The major attractions for music-loving audiophiles are convenience and the
tantalizing prospect of high-resolution audio at 24/96 and higher. We
are on the brink of master tape quality audio a mere keyboard
stroke away. Many online music retail sites and labels already offer high-resolution
downloads. In my own perfect little world, all recorded music would be
available online for downloads at various quality levels. If MP3 sounds fine to
you, download an album for perhaps $5. Want CD quality? Then it’s $10.
Want 24/192? It’s yours for $20 and so on. Leave the issue of quality to the
consumer. Since there's no need to carry multiple physical formats and server
space is cheaper than dirt, cost to the record/retail industry should no longer be
an issue as it was with CD, SACD, DVD-A and LP. Some labels
are already doing that. Linn Records is one example of what
the future may hold. Their website offers most if not all of
their titles and those of several other labels for download and DRM-free at
several levels of fidelity.

While the software is here already and becoming increasingly easier to access,
file playback is still in its infancy. The big present obstacle is
playing those wonderful 24/192 tracks in native bit and sampling rates. You can buy a music server of course but the notion of paying a five-figure sum for
a gold-plated audiophile music server is absurd to folks like me. The Linn Klimax
DS and Bladelius Embla recently reviewed in these pages are perfect examples of
what to avoid - as are several others. Regardless of
asking price, many suffer reliability issues, non-existent upgrade
options or poor user interfaces. Playing music should be simple and not require a
PhD in computer science. Nor eagle eyes to read dinky little displays.
Muddying the waters further is the bewildering array of options - music
streamers, servers, isochronous and asynchronous USB DACs, sound cards,
Ethernet, WiFi and disc players with various digital inputs. Ay caramba! To the uninitiated, it’s quite confusing. That said, I am thus far impressed with PS Audio’s clever new Perfect Wave
series which appears to be an excellent and still affordable option. Too
bad the PWT has such a tiny screen. My advice is to wait until the technology
matures. Perhaps go the DIY route for now with an existing laptop/desktop
and DAC.

However, the challenge of high-resolution playback remains. While there are
affordable sound cards, most don't allow for higher than 96kHz
sampling rates and require a desktop PC with an open slot.
Those cards won’t help laptop users and external ones I’ve
seen retail at or well over $1,000.

I also have concerns about the sound quality of
various cards considering they generally run wimpy power supplies, poor
analog output stages and seem quite prone to jitter. What’s the point of 24/192
conversion if the music signal is corrupted by excessive jitter and noise artifacts?

There are a number of USB DACs and USB-to-S/PDIF converters for use with
legacy DACs. Still, most are limited to 24/96 or even 16/48 and prone to higher jitter
rates. Some like the Weiss Minerva will do 24/192 but require a
Firewire capable computer. For PC users, there’s the issue of the dreaded Windows
kernel mixer to interfere with music playback. There
of course are a number of methods to get around it such as ASIO or kernel streaming. Mac
users don’t have this issue but apparently others.
There are several jitter-resistant 24/192 asynchronous USB
DACs from Ayre, Bel Canto, dCS and
Wavelength Audio. Many folks have mistakenly believed that USB is inherently
limited to 16/44 or 16/48. It turns out that this was more an issue of USB receiver coding than
any physical limitations in the hi-speed USB2 format. If like me you are quite happy with your
current DAC but want to get into the high-rez game without blowing the
monthly mortgage payment, Italian-based M2Tech has you covered.
Their hiFace 24-bit/192kHz USB interface looks like an
oversized memory stick with your choice of RCA or BNC jack
attached at the other end. By using proprietary drivers, the hiFace transmits
high-resolution audio in native mode up to 24/192 right off your laptop or desktop
out to a 24/192 capable DAC with the least possible amount of jitter. Moreover,
you don't need a fancy USB cable. Your existing digital cable will suffice.
With its proprietary driver, the hiFace appears to your computer as an
USB audio card capable of passing 24/192 data streams. Slick.

While easy to install and configure, the hiFace is not a plug and play device. It does
require some computer knowledge. The hiFace ships with detailed setup
instructions and M2Tech’s website has a comprehensive FAQ and troubleshooting
guide should you run into trouble. For Windows users it’s simply a
matter of selecting the hiFace in your Windows Sounds and Audio Devices
Properties tab followed by selecting the kernel streaming mode in the options tab
of whatever compatible music player you chose.
At present, hiFace is compatible with Mac OS 10.4, 10.5 & 10.6 and Windows
XP, Vista and 7.
The hiFace operates asynchronously with two low-jitter quartz precision oscillators
covering the multiples of 44.1kHz and 48kHz, i.e. 88.2/176kHz and 96/192kHz
respectively. M2Tech claims very low jitter and phase noise. A pulse transformer
provides galvanic isolation from the computer. Currently support is limited to Windows
and Mac operating systems. Support for Linux is forthcoming.

Since hiFace uses kernel streaming with Windows, you need a compatible player like Foobar, Winamp or Media Monkey. I used
Foobar with its kernel streaming plug-in downloadable at no cost.
However, with the latest drivers hiFace also works—albeit with lesser sound
quality—in direct sound mode. Any player is usable provided it was set up
to use direct sound. This allows for Internet radio streams, Windows
and game sounds like a regular sound card. For Vista and Windows 7
users, M2Tech recently released a new driver compatible with WASAPI
for bit-perfect transfer with players that do not support kernel
streaming. Hence your choice of music playback is not limited to the
three players mentioned for bit-perfect transfers.

According to M2Tech, Windows XP—even Vista and 7 to an extent—run the kernel mixer (Kmixer) software which manages audio streams
towards peripherals dedicated to their conversion. The kernel mixer comes into
play each time a player interacts with a peripheral in direct sound mode.
Currently this is the only mode in which Windows Media Player operates. The
kernel mixer processes the audio stream by modifying the sound samples. It
performs two format changes from integers (the format of almost all
audio files) to floating point and back again. This introduces
unavoidable approximations due to the finite length math in all processors. It produces noise and increased distortion to compromise sonics. The kernel mixer also puts a heavy load on the CPU
which in direct sound mode can approach 100%. A
considerably better way of interfacing player and peripheral is kernel streaming to bypass the dreaded Kmixer altogether. While drivers can allow kernel-streaming peripherals to
operate in direct sound mode, these drivers also load the CPU. For this
reason, not all PCs can reproduce audio files higher than 48kHz. Moreover,
these drivers are not available for all peripherals.

The M2Tech hiFace uses a proprietary driver to interact directly with a player in
kernel streaming mode at a low level of CPU loading. It does so without any other drivers and
allows for audio data to reach the peripheral easily and without any undesired
changes to the data stream. That's the long way of saying that your computer will pass
a bit-perfect 24/192 data stream without bogging down your machine or
screwing with the sound. The other option of course is to buy a Mac and use
iTunes. Some folks suggest that is sonically superior and easier to use than
most PC/Windows combinations.
M2Tech meanwhile claims superior jitter rejection by using two high-stability low-noise
crystal oscillators as opposed to the ubiquitous PLL (phased lock loop) circuit.
Jitter is essentially short-term variations of the sampling frequency which we now
understand to be partially responsible for some of the sonic limitations in digital
playback.

According to M2Tech, the hiFace offers jitter stability of 2.5ppm to
translate into a sampling frequency error rate of no more than 2.5Hz for every
MHz of output frequency. Therefore, the maximum error at 192kHz will be .5Hz
whereas a PPL could be off nearly 10kHz! M2Tech states, "...we think we’re
listening to the right sampling frequency but actually we’re listening to a different
sampling frequency and all instruments are out of tune." With the hiFace
connected to a computer, the S/PDIF receiver of the downstream DAC should
recover a more stable and accurate clock signal, hence deliver a more enjoyable
listening experience. I suspect this jitter issue is why I have been unimpressed
by USB DACs to date.